1. Field of the Invention
This invention relates to personal identification systems and more particularly to such systems wherein a personal identification number known only to the bearer of a card and a number on the card are utilized for identifying the bearer.
2. Description of Prior Art
Personal identification systems utilizing an account number read from a credit card and a personal identification number (PIN) known only by the authorized bearer of the card are well known in prior art. For example, in U.S. Pat. No. 3,657,521, which issued to Jeffrey Constable on Apr. 11, 1972, on an application filed Aug. 24, 1970, there is disclosed a system in which a linearfeedback shift register is utilized to encode an account number onto a credit card. The account number is a predetermined function of the secret personal identification number. When a customer wants to make a transaction, identification is accomplished by comparing the keyed-entry of the personal identification number with the account number read from the credit card. The account number is translated by an enciphering unit before the comparison with the keyed-in personal identification number. The translation involves filling a shift register which is provided with feedback to adders so as to generate the digits of a translated number successively. The translated number is compared with the corresponding digits of the keyed-in personal identification number. Since the translation is the reverse of the enciphering process which recorded the number originally on the card, the translated number should correspond to the personal identification number.
While the personal identification number cannot be derived from the number recorded on the credit card without having access to the translating circuitry, it is possible that a criminal could obtain information about the translating circuitry and thus be able to derive the personal identification numbers from stolen credit cards.
Another prior approach is that disclosed in U.S. Pat. No. 3,938,091 which issued on Feb. 10, 1976 to Martin Atalla on an application filed July 19, 1974. In this patent an individual code word or account number is combined with a secret code word or PIN memorized by the card holder to produce a compiled code word. The compiled code word is stored for subsequent use in personal identification. During personal identification the individual code word is read from the credit card and the PIN is inputted by the card holder, the two code words being passed through the encoder to generate the compiled code word. The compiled code word thus generated is compared with the previously stored compiled code word. If the two compare the transaction is authorized.
This approach, while providing more security than the previous approach, is also subject to tampering by criminals which might gain access to the list of compiled code words or to the circuitry for performing the encoding operation.